Interventional Radiology (IR) is a rapidly growing branch of medicine which uses medical imaging systems such as Computer Tomography, Magnetic Resonance, X-ray and fluoroscopy for therapeutic as well as diagnostic purposes. In IR, a physician wishes to guide a catheter to a remote site within the body for the purpose of making measurements, retrieving samples (biopsy), effecting therapeutic actions (for example, angioplasty of an artery wall), or blocking of an artery feeding a tumor (embolization). The catheter is a thin tube (2-6 mm diameter) on the order of 1 meter long which contains a number of interior passages (depending on design) and which is guided by a flexible, removeable, X-ray opaque internal guide wire.
The circulatory system can be thought of as a tree-like structure fanning out from a central arterial tube at the heart. The diameter of the main aorta is on the order of 2-4 cm. Beginning with the bifurcation of the main aorta, each subsequent branch forks or bifurcates into two or more smaller diameter branches. Eventually at the cellular level the arterial diameter narrows to that of an individual red blood cell. The veinous system is responsible for collecting the blood cells from the capillaries for eventual return to the heart. The geometry of the veinous network is the inverse of the arterial system, with small tubes merging to form larger tubes which merge to form still larger tubes. While there is considerable similarity in topology and geometry among individuals at a gross level, at a detailed level the vascular system has a complex topology with a tortuous three-dimensional geometry which is unique to each individual.
The goal of an IR procedure is to deliver the working end of a catheter to an internal site within the body of the patient. The vascular system is used to physically contain the catheter and to act as the conduit along which the catheter progresses. Access to the vascular system is via a puncture with a tubular sleeve which remains in place during the procedure. The catheter and guide wire are threaded through the sleeve.
The fluoroscope (a 30 Hz X-ray machine) is the primary tool used by the physician to help guide the catheter. In many cases, his knowledge of general vascular anatomy, his experience, and the "in-process" fluoroscope images provide sufficient information to enable the physician to reach the target site. Typically, the images are formed at a rate of 30 per second and displayed on a TV-like monitor.
The most prominent feature in a fluoroscopic image is the radio-opaque catheter guide wire. When the guide wire is inserted into the catheter, the thin guide wire shadow in the fluoroscopic image indicates to the physician the location of the catheter. When the guide wire tip is extended beyond the end of the catheter (before the actual catheter is advanced), the guide wire shadow indicates one possible future path of the catheter. Often, due to the amount of tissue through which the X-rays must penetrate or the small size of the guide wire, the guide wire "shadow" is not easily distinguishable from the surrounding tissue.
What is needed is a catheter guide wire enhancement system that would aid the physician in ascertaining the position of the catheter guide wire in fluoroscopic images. The system would create a two-dimensional model of the guide wire in the image plane, and overlay the highlighted two-dimensional model on top of the live fluoroscopic images at a rate of 30 frames per second.
A major benefit of this invention is that a lower dose of X-rays can be used since the radiologist can work with a "poorer" image.